1. Field of the Invention
This invention relates to the casting of metal strip. It has particular application to the casting of metal strip by continuous casting in a twin roll caster.
2. Description of Related Art
In a twin roll caster molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The term "nip" is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel or series of vessels from which it flows through a metal delivery nozzle located above the nip so as to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in sliding engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electromagnetic barriers have also been proposed.
The change-over of the casting rolls in a twin roll caster is a significant problem. The rolls may need to be changed between casts so as to allow a different width of strip to be cast and the rolls must be replaced if the casting surfaces are in any way damaged or deteriorate during casting. If the rolls have to be changed in situ, a significant amount of potential casting time is lost waiting for the casting components and the area surrounding them to cool. The new set of rolls, once in place, has to be calibrated prior to casting so that the nip width can be pre-set.
When casting ferrous metals, it is necessary to preheat the refractory components of the metal delivery and pool confinement means to very high temperatures before casting commences. For these reasons it has been proposed to build twin roll casters with demountable components so that the rolls and preheated refractory components can be rapidly brought together into an operative assembly and casting started before the preheated components cool significantly. One example of a caster with moveable rolls and refractory components is disclosed in our Australian Patents 631728 and 637548 and corresponding U.S. Pat. Nos. 5,184,668 and 5,277,243.
The present invention enables a twin roll strip caster to be built with a modular construction in which the casting rolls are installed in a moveable module readily moveable into and out of the machine. A previous proposal for mounting the rolls on a moveable module is described in Japanese Patent Publication JP-B93-9185 of Mitsubishi Heavy Industries Ltd. In that proposal the rolls and the pool confining side plates are mounted together on a frame which is carried on a wheeled car moveable horizontally into and out of the machine along rails. The present invention provides a different arrangement in which a roll module is moved horizontally into an intermediate position beneath the final casting position and is then lifted into the casting position. This enables the rolls to be quickly manoeuvred into the casting position without requiring movement of any ancillary equipment or components. In a preferred embodiment of the invention the rolls can be lifted into position between a pair of pool confinement side plates without the need to move the side plates.